Generally, in connection with a development of an environmentally friendly vehicle, such as a plug-in hybrid and a hybrid vehicle, a converter for charging an alternating current-direct current (AC-DC) high voltage battery (hereinafter, OBC) may be an essential component. The OBC includes a power factor correction (PFC) converter to improve a power factor. An output terminal of the PFC needs to be provided with a large-capacity output power capacitor to absorb a voltage and current ripple and secure an instantaneous power failure hold-up time. This is schematically illustrated in FIG. 1. Referring to FIG. 1, a PFC converter circuit 110 is configured to include a PFC inductor 111, a PFC output capacitor 112, and the like. Further, the PFC converter circuit 110 is configured to further include an input unit 101, a DC-DC converter 140, a high voltage battery 150, and the like.
Herein, a concept of the hold-up time is briefly represented by the following Equation.½CPFC(VPFC_cap2−Vmin2)=Powerout×THold-up  Equation 1
In the above Equation 1, the left side is proportional to a capacity of a capacitor as energy stored in the PFC output capacitor 112. In the above Equation 1, Vmin is a minimum PFC output voltage which may emit an OBC normal output. That is, to increase the hold-up time in the condition in which the OBC output is fixed, there is a need to increase a capacity C_pfc of the capacitor or a voltage V_pfc_cap applied to the capacitor.
However, since a separate circuit is not generally present in the vicinity of the PFC output capacitor, a voltage level of the capacitor may not be increased at the time of AC power instantaneous power failure. Therefore, to increase the hold-up time, only a method for increasing the capacity of the capacitor has been developed. Further, to reduce the PFC output voltage and/or current ripple, only a method for increasing a capacity of a PFC inductor and capacitor has been developed. This may increase the overall size and cost of the OBC, reduce an output density, and cause a problem of a configuration of a high voltage charging system package.
In other words, to reduce the voltage and current ripple of the output terminal of the PFC, there is a need to increase a magnitude in a capacitance of the output capacitor. However, since the capacitor is generally a component that occupies a largest volume within the OBC, there is a limitation in increasing the capacitance of the capacitor to improve the output density of the OBC. That is, an optimal capacity of the capacitor needs to be selected in consideration of the reduction in the output voltage ripple and/or the reduction in the package size of the OBC.